thyroid hormones Flashcards
thyroid hormone is release in response to
input from cold sensitive neurons
what are the actions of thyroid hormones on the body
increase metabolic rate > increase heat production in most cells (lipid oxidation, carbohydrate metabolism)
stimulate cardiovas sys - increase sensitivity of heart to epi + increase contraction of heart via transcriptional changes
required for normal growth
describe the HPA axis of thyroid hormone release
H releases TRH: Target thyrotrophs in ant pit >ant pit releases TSH: target thyroid gland in periphery. > thyroid gland releases T4 and T3
describe the thyroid gland explain how iodine is added
- found at the top of trachea
- thyroid cells form follicules > contain colloid + thyroglobulin
- iodine is enzymatically added to tyrosine of thyroglobulin
whats the difference between T3 and T4
t3 = 3 iodine t4=4 iodine
T3 more active
T4 is released in greater quantity
T3 is more active but degraded easily so whats the deal
T4 binds to protein in blood better so not degraded as easily > target tissue then converts T4 > T3
describe action of T3/T4
bind intracellular receptors and modulate gene transcription > longer-lasting effects in target tissue
what happens with lack of adequate thyroid H during development
cretinism = mental retardation + unusally short stature
describe hypothyroidsm
Iodine deficiency > lower synthesis of T3/T4
Causes lethargy, fatigue, cold intolerance, and goiter (TSH causes growth)
what is hashimoto disease
autoimmune disorder where immune system destroys thyroid gland > treated with daily administration of synthetic thyroid hormone
what happens with lack of adequate thyroid H during development
cretinism = mental retardation + unusally short stature
describe hyperthyroidsm
Can be caused by pituitary tumor or autoimmune disorder (Grave’s Disease)
Symptoms include anxiety, insomnia, increased HR
Treatment includes drugs that block synthesis of thyroid hormones
whats the negative feedbck of this system
T3/T4 inhibit hypothalamus/ant pi
